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Sulfur/TAN Ratio Effect on Iron Sulfide (FeS) Scale Properties Challenged in Continuous Oil Flow

Picture for Sulfur/TAN Ratio Effect on Iron Sulfide (FeS) Scale Properties Challenged in Continuous Oil Flow
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Naphthenic acids and sulfur compounds are important corrosive species contained in low quality crudes and can cause significant equipment damages when such crudes are processed. Although the two corrosive species have a synergistic effect at high temperatures their corrosion products can influence the extent of the damage. Thus the iron sulfide (FeS) scales formed as sulfur reacts with iron can hinder the NAP acid diffusion to the metal limiting their corrosive effect. The FeS scales properties are influenced by different factors such as the types of sulfur compounds in oil (sulfides disulfides mercaptans thiophenes) NAP acids interactions temperature flow conditions - all factors that are difficult to control. This experimental work intended to evaluate the properties of FeS scales formed from model sulfur compounds (sulfides and mercaptans) in interaction with NAP acids using the “pretreatment – challenge” test protocol. According to this protocol FeS scales were formed on metal samples from mercaptans/mercaptans and sulfides on different ratios/concentrations in the presence of NAP acids at high temperature.Further preformed scales were exposed to a constant NAP acid attack under high temperature and continuous flow conditions. Samples metal losses and scale SEM/EDS analysis were used to characterize the protective properties of FeS scales.Keywords: sulfur model compounds naphthenic acid corrosion high temperature

Product Number: 51319-13490-SG
Author: Gheorghe Bota
Publication Date: 2019
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Phosphate Esters Inhibitors in Naphthenic Acid Corrosion – An Experimental Evaluation

Product Number: 51319-13491-SG
Author: Gheorghe Bota
Publication Date: 2019
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Crude oils with a total acid number (TAN) higher than 0.5 are highly corrosive at temperatures between 400 and 700°F typical to atmospheric and vacuum distillations of oil refineries. This destructive effect of naphthenic acids (NAP) is enhanced by the presence of hydrogen sulfide generated in thermal decomposition of sulfur compounds also contained in crude oils. The efforts of mitigating the acidic crudes corrosive effects include blending such oils with crudes of lower acids content neutralization or removal of naphthenic acids from oils and the use of corrosion inhibitors. Most commonly used inhibitors for mitigating the NAP corrosion are based on organic polysulfides or on phosphate esters. Two phosphate esters corrosion inhibitors were evaluated in laboratory experiments using a specific testing procedure – “pretreatment - challenge”. This experimental method evaluates the naphthenic corrosive effects at high temperature on scales formed from crude factions on metal surfaces. Adding the inhibitors to the crude fractions improved the protective properties of scales formed under such conditions. The corrosive effect of naphthenic acid was evaluated by sample weight loss. The scales formed on these samples were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) coupled with energy dispersive spectroscopy (EDS).Keywords: phosphate esters corrosion inhibitors naphthenic acids high temperature
Picture for New Approach on Iron Sulfide Scale Modeling and Prediction at pH 4-7
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New Approach on Iron Sulfide Scale Modeling and Prediction at pH 4-7

Product Number: 51320-14532-SG
Author: Xin Wang, Saebom Ko, Alex Yi-Tsung Lu, Guannan Deng, Yue Zhao, Chong Dai, Samridhdi Paudyal, Amy T. Kan, Mason B. Tomson
Publication Date: 2020
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In this study, a plug flow reactor was built to investigate iron sulfide scale precipitation at various temperatures, pH and ionic strength conditions and two pieces of carbon steel C1018 coupons were put inside as reaction surfaces. The ferrous ion and total sulfide in collected effluent samples were measured to determine precipitation kinetics and solubility. The solid that formed on the steel surfaces were analyzed by Scanning Electron Microscopy (SEM/EDS) and X-ray Diffraction (XRD). The solubility data from this study and literature were collected and fitted by Matlab to build up a reliable FeS solubility prediction model. The experimental results show that mackinawite is the predominant precipitated scale and could be stable for a week at pH higher than 6.0. Iron sulfide precipitation is under diffusion control, accelerated by high temperature and ionic strength. At pH 6 – 7, the aqueous phase neutral species, such as 𝐹𝑒𝑆0𝑎𝑞, plays an important role in the solubility and precipitation kinetic. Based on this study, a new solubility model that combines Pitzer theory and ion-complexes (speciation of ferrous ion) has been developed for iron sulfide solubility calculation and scale prediction. 
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98143 EFFECT OF FLOW VELOCITY ON CRACK INITIATION

Product Number: 51300-98143-SG
ISBN: 98143 1998 CP
Author: S. Hettiarachchl, T.P. Diaz, G.P. Wozadlo, J.E. Weber, K.S. Ramp
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